Nominal Performance Recovery Research Articles

Adaptive High-Gain Observer-Based Control for Grid-Tied LCL Filter Systems

This paper presents the design and real-time implementation of a composite controller consisting of a state-feedback control law and high-gain observer for grid-tied inverter with <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCL</i> filter. The state-feedback controller is designed in the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$dq$</tex-math></inline-formula> reference frame to stabilize the closed-loop system. High-gain observer serves as a disturbance observer to estimate a fictitious variable, representing the effect of model uncertainties and unknown disturbances, which is then canceled by the state-feedback controller. Thus, asymptotic regulation can be guaranteed under the composite controller even in the presence of parametric uncertainties and unknown inputs. High-gain observer has a rate of convergence that is dependent on its gain which is required to be large enough to ensure fast disturbance estimation, and then nominal performance recovery. However, high observer gain can lead to poor steady-state performances due to the effect of measurement noise. This concern is overcome in this work by using an existing adaptive technique to adjust the observer gain on-line. Moreover, the resulting high-gain observer is further simplified to provide a less-complex estimator and to show its integral action property. The performance of the composite controller was experimentally tested. The obtained results demonstrated the ability of the proposed controller to meet the nominal performance specifications while reducing the effect of measurement noise in steady-state.

Time bound online uncertainty estimation based adaptive control design for DC–DC buck converters with experimental validation

In this paper, an adaptive controller is proposed for DC–DC buck converters featuring prescribed time bound estimation of unknown system uncertainties and exogenous disturbances followed by nominal output performance recovery. The objective of the proposed control is to attain a robust output voltage tracking in buck converter in presence of parametric, non-parametric, matched and mismatched perturbations across wide operating range. Different from neural network estimators and characterizing substantially low computational complexity, an online estimator is presented to reconstruct the incurred uncertainty. The estimated additive uncertainty is thereafter fed to the nominal backstepping controller for subsequent compensation in finite time. Exact recovery of nominal output voltage tracking is claimed in a piecewise sense owing to the accuracy and precise estimation of the unknown unparametrized lumped uncertainty manifested in the form of large sudden variations in load and input voltage. Rigorous performance and stability analysis of the online estimator, along with similar analysis of the overall tracking control system are undertaken. Extensive numerical study is carried out to investigate the performance of the proposed control scheme. Further, experimentation of the proposed controller on a dc–dc buck converter using control desk DS1103 with an embedded TMS320F240 processor has been performed. The obtained experimental results demonstrate a good agreement with the simulation findings.

A Real-Time Performance Recovery Framework for Vision-Based Control Systems

The demand for high performance of vision-based control systems is ever increasing. This article, thus, proposes, for the first time, a real-time performance recovery framework for the vision-based control of highly dynamic systems. The framework enables functionalized nominal controller and performance recovery, balanced image processing, and performance recovery, as well as enhanced real-time efficiency, which is based on the observer-based realization of the Youla parameterization of all stabilizing controllers. An online learning algorithm for real-time performance recovery against the unexpected performance degradation is developed as well. The verification of the proposed framework and algorithm promises their applications to classes of vision-based highly dynamic control systems.

Robust Limit Cycle Generation in Nonlinear Dynamical Systems With Nominal Performance Recovery

Abstract This paper proposes a disturbance observer (DO)-based method for shaping robust limit cycles in a class of uncertain nonlinear systems. The modified Lyapunov theorem is utilized to shape desirable limit cycles in the nominal system. Then, a high-gain filter is designed to robustify the controller and add the nominal performance recovery capability to it. It is proved that the trajectories of uncertain system coincide with those of the nominal system. The effective performance of the proposed controller is illustrated by simulation.

Decoupled PI current controller for grid‐tied inverters with improved transient performances

This study proposes a novel decoupled proportional–integral (PI) current controller for grid-tied inverters. The proposed controller can be viewed as the modification of the existing decoupled PI current controller to include the reference jump in order to achieve nominal performance recovery in response to step changes in the current reference. The modified decoupled PI current controller is derived based on combining feedback-linearisation technique with a disturbance observer-based control approach that belongs to the high-gain observer technique. The key feature of the composite controller is its ability to retain the transient performance specified under the feedback-linearising control, particularly when the control does not saturate. Furthermore, by considering the control saturation in the observer design, an anti-windup scheme arises naturally into the controller, leading to an improved transient performance in the presence of saturation. The effectiveness of the proposed controller was verified by simulation and experimental results.

A Novel Design of PI Current Controller for PMSG-Based Wind Turbine Considering Transient Performance Specifications and Control Saturation

This paper presents a novel design process of decoupled PI current controller for permanent magnet synchronous generator (PMSG)-based wind turbines feeding a grid-tied inverter through a back-to-back converter. Specifically, the design methodology consists of combining disturbance observer-based control (DOBC) with feedback linearization (FBL) technique to ensure nominal transient performance recovery under model uncertainty. By simplifying the DOBC under the feedback linearizing control, it is shown that the composite controller reduces to a decoupled PI current controller plus an additional term that has the main role of recovering the nominal transient performance of the FBL, especially under step changes in the reference. Additionally, an antiwindup compensator arises naturally into the controller when considering the control input saturation to design the DOBC. This permits removal of the effect of the saturation blocks required to limit the control input. The proposed control scheme is implemented and validated through experimentation conducted on 22-pole, 5 kW PMSG. The results revealed that the proposed technique can successfully achieve nominal performance recovery under model uncertainty as well as improved transient performances under control saturation.

Experimental Validation of a Novel PI Speed Controller for AC Motor Drives With Improved Transient Performances

A proportional–integral (PI) controller is the most frequently used control technique for adjustable speed-motor drives. The main advantage of a PI controller is its ability to ensure zero steady-state error under low-frequency disturbances and model uncertainties as long as the closed-loop system is stable. However, the transient performances, under a PI regulator, are highly dependent on the machine parameters, the external disturbances, and the input constraints. This brief proposes the design process of a novel PI speed controller that is capable of preserving almost the nominal transient performance under the parameter variation and external disturbances such as the load torque. The controller also suppresses the effect of input saturation that may occur because of the armature current limitation. Simulation and experimental tests are carried out to verify the validity of the proposed design process. The results revealed that the proposed PI controller is effective regarding nominal performance recovery and input constraints handling.

Multivariable Finite Time Attitude Control for Quadrotor UAV: Theory and Experimentation

The attitude control of quadrotor unmanned aerial vehicle (UAV) is investigated. The aim of this paper is to develop a continuous multivariable attitude control law, which drives the attitude tracking errors of quadrotor UAV to zero in finite time. First, a multivariable super-twisting-like algorithm (STLA) is proposed for arbitrary order integrator systems subject to matched disturbances. A discontinuous integral term is incorporated in the control law in order to compensate the disturbances. A rigorous proof of the finite time stability of the close-loop system is derived by utilizing the Lyapunov method and the homogeneous technique. Then, the implementation of the developed method in an indoor quadrotor UAV is performed. The remarkable features of the developed algorithm includes the finite time convergence, the chattering suppression and the nominal performance recovery. Finally, the efficiency of the proposed method is illustrated by numerical simulations and experimental verification.

Adaptive Regulation to Nominal Response for Uncertain Mechanical Systems and Its Application to Optical Disk Drive

In this paper, we present an add-on type robust controller for uncertain mechanical systems with a sinusoidal disturbance of an unknown frequency. The main purpose is to recover (predefined) nominal tracking performance in an “asymptotic” sense, that is, the actual output asymptotically converges to the nominal trajectory, as well as the maximum difference between them is maintained small enough during the operation. As a key component of the proposed controller, a disturbance observer that contains an internal model is proposed. Especially, the parameters of the internal model are updated in an “adaptive” fashion in order to cope with the unknown frequency of the disturbance, for which a frequency identifier is employed in the controller design. The nominal performance recovery of the proposed controller is analyzed in the sense of Lyapunov and singular perturbation theory. Both simulation and experimental results point out that the proposed control scheme can serve as a robust track following controller for uncertain optical disk drive systems where eccentricity of disk causes a sinusoidal disturbance.

Nonlinear Disturbance Observer-Based Control for a Class of Port-Controlled Hamiltonian Disturbed Systems

In this paper, a composite control scheme is presented to asymptotically stabilize a class of port-controlled Hamiltonian systems under nonvanishing disturbances. First, based on the damping injection method and the nonlinear disturbance observer (NDOB) technique, the robust composite control strategy is designed. The NDOB, as an effective observation tool, is developed to estimate the disturbances, and furthermore, the disturbances can be feedforward compensated using the estimates of disturbances. Then, for the augmented system, an asymptotic stability theorem is proposed via an input-to-state stability technique and Lyapunov stability theorems. The proposed control approach exhibits not only good robustness and disturbance rejection performances but also the property of nominal performance recovery. Finally, a simulation example on a circuit system is given to show the feasibility and advantage of the composite control method.

Design and Implementation of a Nonlinear PI Predictive Controller for a Grid-Tied Photovoltaic Inverter

This paper presents the design, implementation, and performance testing of a nonlinear proportional-integral (PI) predictive controller for a grid-tied inverter used in photovoltaic systems. A conventional cascade structure is adopted to design the proposed controller, where the outer loop is used to regulate the dc-link voltage, and the inner loop is designed as a current controller for adjusting the active and reactive powers injected into the grid. For each loop, the controller is derived based on combining a continuous-time nonlinear model predictive control and nonlinear disturbance observer techniques. It turns out that the composite controller reduces to a nonlinear PI controller with a predictive term that plays an important role in improving tracking performance. The salient feature of the proposed approach is its ability to approximately preserve the nominal tracking performance during the startup phase. Both simulation and experimental results are provided to demonstrate the effectiveness of the proposed approach in terms of nominal performance recovery, disturbance rejection, and current control.

Finite-Time Stabilization for a Class of Nonlinear Differential-Algebraic Systems Subject to Disturbance

In this paper, finite-time stabilization problem for a class of nonlinear differential-algebraic systems (NDASs) subject to external disturbance is investigated via a composite control manner. A composite finite-time controller (CFTC) is proposed with a three-stage design procedure. Firstly, based on the adding a power integrator technique, a finite-time control (FTC) law is explicitly designed for the nominal NDAS by only using differential variables. Then, by using homogeneous system theory, a continuous finite-time disturbance observer (CFTDO) is constructed to estimate the disturbance generated by an exogenous system. Finally, a composite controller which consists of a feedforward compensation part based on CFTDO and the obtained FTC law is proposed. Rigorous analysis demonstrates that not only the proposed composite controller can stabilize the NDAS in finite time, but also the proposed control scheme exhibits nominal performance recovery property. Simulation examples are provided to illustrate the effectiveness of the proposed control approach.

Finite-Time Reentry Attitude Control Based on Adaptive Multivariable Disturbance Compensation

The finite-time tracking control for reusable launch vehicle with unmatched disturbance is investigated. An adaptive-multivariable-disturbance-compensation scheme is proposed to provide the estimation for external disturbances where the bounds of the perturbations are not known. Based on the estimation, a continuous multivariable homogeneity second order sliding mode controller is designed to ensure that the attitude tracking is achieved in finite time. A proof of the finite-time convergence of the closed-loop system under the integrated controller and disturbance observer is derived using the Lyapunov technique. The features of the proposed control scheme are that it does not require any information on the bounds of the disturbance and its gradient except for their existence. At the same time, the finite-time convergence, nominal performance recovery, and chattering alleviation are guaranteed. Finally, some simulation tests are provided to demonstrate the effectiveness of the proposed control scheme.

필터 삽입에 의한 외란 관측기의 성능 향상과 하드디스크 장치에의 적용

In this paper, we present a new control structure which is obtained by adding an appropriately designed filter to a conventional disturbance observer. The proposed controlled system preserves advantages of a system with the conventional disturbance observer; disturbance rejection and nominal performance recovery. In particular, by embedding the filter, the disturbance rejection performance is enhanced compared with that of the classical disturbance observer-based controlled system. Moreover, we suggest a condition for the robust internal stability of the considered system in this paper. Simulation results regarding an effect of relatively high-frequency disturbance on hard disk drive are also presented.

Design of a Prediction-Accuracy-Enhanced Continuous-Time MPC for Disturbed Systems via a Disturbance Observer

This paper addresses the prediction accuracy enhancement problem in the context of continuous-time model predictive control (MPC) by using a disturbance observer. The disturbance estimation is introduced in the output prediction to correct the errors caused by disturbances and uncertainties, which eventually leads to the desired offset-free tracking performance. Due to such a different design philosophy, the computational burden of the proposed method will be significantly reduced as compared with the existing offset-free MPCs for disturbed systems. Another promising feature of the proposed method lies in its nominal performance recovery property. The workability of the proposed method is validated by its application to a dc–dc buck converter system.

Super-Twisting Algorithm for DC Motor Position Control via Disturbance Observer

This paper develops a Super-Twisting Algorithm controller via a nonlinear disturbance observer for a DC motor system subject to matched and unmatched uncertainties. The proposed controller is based upon a novel Nonlinear Disturbance Observer structure which uses the concept of total disturbance estimation in order to estimate simultaneously the matched and the unmatched uncertainties in the system. This estimation is incorporated then in a composite observer based controller where the stability analysis is given. Simulations results illustrate the effectiveness of the proposed controller compared to other some existing control designs and show its advantages in terms of disturbance rejection, nominal performance recovery and chattering reduction.

Non‐linear disturbance observer‐based back‐stepping control for airbreathing hypersonic vehicles with mismatched disturbances

This study concerns with robust tracking control problem for the longitudinal model of airbreathing hypersonic vehicles (AHVs). The AHVs include serious non-linearities, strong couplings, parametric perturbations and mismatched disturbances, which results in great difficultly in the controller design. By using back-stepping method and non-linear disturbance observer technique, a novel composite controller is proposed, which can guarantee system outputs asymptotically track their reference signals. A new idea is that disturbance estimations are introduced into virtual control law in each step to compensate the mismatched disturbances. As compared with other robust flight control methods for AHVs, the developed method exhibits not only excellent robustness and disturbance rejection performance but also the property of nominal performance recovery. Finally, the effectiveness of the proposed method is demonstrated by simulation results.

Offset-Free Nonlinear MPC for Mismatched Disturbance Attenuation With Application to a Static Var Compensator

A generalized nonlinear model predictive control augmented with a disturbance observer is proposed in this brief to solve the disturbance attenuation problem of nonlinear systems with arbitrary disturbance relative degree. It is shown that the disturbances can be removed from the output channels by the proposed method with appropriately designed disturbance compensation gain. The property of nominal performance recovery is retained with the proposed method. The effectiveness of the proposed method is validated by applying it to a static var compensator system.

Continuous finite-time anti-disturbance control for a class of uncertain nonlinear systems

The continuous finite-time anti-disturbance control problem for a class of nonlinear system under external disturbances and parameter uncertainties is investigated in this article. First, a continuous terminal sliding mode control (CTSMC) is introduced to stabilize the nominal system dynamics. Concerning the unsatisfying performance of the CTSMC in the presence of severe external disturbances and parameter uncertainties, a finite-time disturbance observer (FTDO) is employed to estimate the uncertainties to its nominal dynamics. By integrating the CTSMC method with the FTDO technique, a composite controller is presented for such kind of nonlinear system under external disturbances and parameter uncertainties. The composite controller obtains finite-time convergence property in the presence of disturbances and also nominal control performance recovery in the absence of disturbances. Moreover, compared with conventional sliding mode control, the proposed control law is continuous and no chattering phenomenon exists. The property of stability and the finite-time convergence of the closed-loop system under the proposed controller is guaranteed by means of Lyapunov stability criteria. The proposed control method is finally applied for the tracking control problem of robotic manipulators. Simulation results show that the proposed method exhibits promising control performance in the presence of severe external disturbances and parameter uncertainties.

Continuous nonsingular terminal sliding mode control for systems with mismatched disturbances

A continuous nonsingular terminal sliding mode control approach is proposed for mismatched disturbance attenuation. A novel nonlinear dynamic sliding mode surface is designed based on a finite-time disturbance observer. The time taken to reach the desired setpoint from any initial states under mismatched disturbance is guaranteed to be finite time. In addition, the proposed method exhibits the fine properties of nominal performance recovery as well as chattering alleviation.